1. Field of the Invention
The present invention relates to a two-stroke engine.
2. Description of the Related Art
To obtain a good loop scavenging operation in the combustion chamber of a known two-stroke diesel engine, a masking wall is provided for masking the valve opening between the valve seat and the peripheral portion of the intake valve, which is located on the cylinder axis side, and, at the same time, masking the valve opening between the valve seat and the peripheral portion of the exhaust valve, which is located on the cylinder axis side, when the valve lifts of the intake valve and the exhaust valve are small. The intake port and the exhaust port are arranged to extend upward in parallel to the cylinder axis (U.S. Pat. No. 4162662). In this two-stroke diesel engine, air flowing into the combustion chamber from the intake port flows toward the top face of the piston along the inner wall of the cylinder. Subsequently, the flow direction of the air on the top face of the piston is changed, and the air then made to flow toward the exhaust port along the inner wall of the cylinder, to thereby carry out a loop scavenging operation.
In this two-stroke diesel engine, however, when the valve lifts of the intake valve and the exhaust valve become large, the valve opening between the intake valve and the valve seat is open to the combustion chamber over the entire periphery of the intake valve, and the valve opening between the exhaust valve and the valve seat is open to the combustion chamber over the entire periphery of the exhaust valve. As a result, air flowing into the combustion chamber from the valve opening of the intake valve, which is located on the cylinder axis side, moves forward along the inner wall of the cylinder head and is then discharged into the exhaust port via the valve opening of the exhaust valve. Consequently, in this two-stroke diesel engine, since a part of the air fed from the intake port must be used to ensure an effective loop scavenging operation, a problem occurs in the engine in that a good scavenging operation cannot be obtained.